(a) Field of the Invention
The present invention relates to an organic light emitting device which can improve optical efficiency by having a photonic crystal structure, and a manufacturing method thereof.
(b) Description of the Related Art
Organic light emitting devices (OLEDs) are self-luminescent devices that emit light when electrons and holes are combined in a fluorescent or phosphor organic layer when current flows to the fluorescent or phosphor organic layer. OLEDs can be manufactured to be lightweight using less number of components through a simple manufacturing process, and can provide high-quality images and wide-view angles.
In an OLED, the external light emission efficiency becomes a standard for deciding the light emission efficiency of a product. The external light emission efficiency of the OLED is determined by the internal quantum efficiency and the optical coupling efficiency. The internal quantum efficiency is determined by the nonradiative recombination loss and the singlet-triplet branching ratio. The internal quantum efficiency can be improved to 80% experimentally. On the contrary, it is recognized that the optical coupling efficiency is improved to 20% because it is relatively quite low compared with the internal quantum efficiency. Accordingly, the research to improve optical coupling efficiency is under way, and the development of related technologies is steadily progressing.
A total reflection occurring at an interface of each layer of the organic light emitting device is a major factor lowering the optical coupling efficiency. The organic light emitting device is formed of a plurality of air layers. The total reflection occurs mostly at interfaces of the air layers. Conventionally, there are various known techniques for preventing total reflection and improving optical coupling efficiency.
Conventionally, there are known a method for patterning a silica microsphere on a substrate, a method for patterning a microlens on the back surface of a substrate, and a method for patterning a photonic crystal structure on a substrate by an etching process. Such techniques improve optical coupling efficiency by scattering light at a substrate or at an interface of each air layer. In the techniques that have been thusly studied and reported or known, light emission efficiency is improved by forming a pattern of nanometer size. However, these known techniques are the result of the experiment carried out on samples of areas of several mm size in order to form a nanometer size pattern. Therefore, in the case of actually manufacturing an organic light emitting device product, it is difficult to form a nanometer level pattern, and its manufacturing cost is high.
In addition, conventionally, there is known a result of improving light emission efficiency by using an AAO (Anodic Aluminum Oxide) film having holes of 400-450 nm. However, the method using an AAO film has a number of problems including difficulty of manufacturing a large-area thin film and low productivity. Moreover, the process using an AAO film is problematic in that it is difficult to apply the process to a plastic substrate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.